Splenic marginal zone B-cell lymphoma (SMZBCL) is a rare non-Hodgkin B-cell lymphoma that presents with morphologically mature lymphoid cells corresponding in their immunological characteristics to secondary follicular marginal zone lymphocytes. It is clinically characterized by splenomegaly, moderate lymphocytosis, usually focal bone marrow lesion, sometimes moderate of monoclonal immunoglobulin in the serum (generally IgM or IgG) and/or urea, and a relatively benign course. Leishmaniasis is a transmissible natural focal infectious endemic disease that has a great diversity of clinical manifestations. The authors describe Russia’s first case of SMZBCL concurrent with visceral leishmaniasis in a 52-year-old female patient admitted to a hematology hospital with weakness, splenomegaly, and lymphadenopathy. The simultaneous detection of lymphoma and leishmaniasis in the same biopsy specimen is extremely rare. Visceral leishmaniasis should be borne in mind as an opportunistic infection in patients with malignancies, particularly in immunocompromised persons who live or have stayed in the endemic areas.